Heart failure is a prevalent disease affecting millions of American people. The transition from compensated hypertrophy to cardiac failure is often accompanied by apoptotic death of cardiomyocytes but the mechanism and physiological relevance of this phenomenon is not clear. The objective of the proposed studies is to elucidate the signaling pathways responsible for apoptosis in cardiac myocytes and to test their involvement in heart failure. Specifically we will test the hypothesis that members of the stress activated MAP kinase (SAP kinase) cascade, cJun N-terminal kinase (JNK) and p38 kinase, mediate the cardiac hypertrophy and apoptosis induced by increased expression of the alpha subunit of the heterotrimeric G-protein Gq both in vitro and in vivo. The possible involvement of the ICE/caspase family of proteases in the apoptotic response will also be assessed in order to test their potential therapeutic effectiveness in heart failure. The first specific aim utilizes cultured neonatal rat ventricular myocytes as a model system. Myocytes infected with adenoviral vectors expressing wild type or constitutively activated Galphaq manifest features of hypertrophy (increased ANF expression, cell enlargement, myofilament organization) with a progression to apoptotic cell death (chromosomal fragmentation and nuclear condensation). The proposed studies will analyze the sequential development of hypertrophy and apoptosis and its relationship to the strength of Galphaq signaling, the involvement of downstream SAP kinase and the relationship of these responses to caspase activation. The second specific aim utilizes transgenic animals expressing both Galphaq and dominant negative mutant SAP kinase to determine specific roles of the SAPK in Galphaq induced hypertrophy. In the third specific aim, the same group of mice will be experimentally manipulated by transverse aortic banding, infusion of agonists or pregnancy in order to determine the role of SAPKs in the induction of apoptotic heart failure as observed in Galphaq transgenic mice under these experimental manipulations. In the final specific aim, constitutively active upstream activators of JNK and p38, shown to induce hypertrophy and apoptosis in cultured myocytes, will be conditionally expressed in hearts of transgenic mice. Changes in cardiac function and morphology resulting from the expression of the activated upstream activators of SAPK will be analyzed. If apoptosis occurs, caspase inhibitors will be administered to test in vivo their involvement in apoptosis and the relationship of apoptosis to heart failure Overall these studies should contribute to our understanding of the mechanisms by which hypertrophy transitions to heart failure and ultimately to the identification of potentially useful therapies to prevent or reverse the decompensation process.